Comsol Cookbook

7/30/2019 Comsol Cookbook

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Sakari's Quick

Cookbook for

Multiphysics

Modeling

Version 2007-01-15 Comsol Oy, 2007

Sakari's Quick Cookbook for Multiphysics Modeling Page 1


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Table of Contents

1 Selecting Application Modes........................................................................................................... 3

1.1 Heat Transfer, 2D..................................................................................................................... 3

1.2 Heat Transfer, 3D..................................................................................................................... 31.3 Standard Package, Application modes......................................................................................3

1.4 Heat Transfer Module, Application modes...............................................................................4

2 Geometry Modeling and CAD Tools............................................................................................... 5

2.1 Importing CAD Drawing..........................................................................................................5

2.2 CAD Import Options................................................................................................................ 5

2.3 Exporting Geometry (DXF)......................................................................................................5

2.4 Adding Geometric Objects....................................................................................................... 5

2.5 Modifying Objects....................................................................................................................6

2.6 Object Composition.................................................................................................................. 6

2.7 Specifying Grid and Axes.........................................................................................................6

2.8 Using Work Planes................................................................................................................... 62.9 Using Assemblies..................................................................................................................... 6

2.10 Visualization Tools................................................................................................................. 7

3 Modeling Physics and Equations......................................................................................................7

3.1 Entering Material Properties.....................................................................................................7

3.2 Specifying Boundary Conditions..............................................................................................8

3.3 Specifying Application Mode Properties..................................................................................9

4 Meshing.......................................................................................................................................... 10

4.1 Triangular (free) meshing.......................................................................................................10

4.2 Quadrilateral (brick, mapped) meshing................................................................................. 10

4.3 Other Meshing options............................................................................................................10

5 Solving the Model.......................................................................................................................... 11

5.1 Solver settings.........................................................................................................................11

5.1.1 Stationary solver settings................................................................................................ 11

5.1.2 Time-dependent solver settings...................................................................................... 12

5.1.3 Parametric solver settings............................................................................................... 13

5.2 Solver Manager.......................................................................................................................13

5.3 Quick and Easy Solutions.......................................................................................................14

6 Postprocessing and Visualization...................................................................................................15

6.1 Plot Parameters....................................................................................................................... 15

6.2 Creating Animations...............................................................................................................17

7 Documentation and Model Management....................................................................................... 187.1 Creating HTML Summary......................................................................................................18

7.2 Adding Model Description..................................................................................................... 18

7.3 Adding Model Image..............................................................................................................18

7.4 Maintaining User Model Library............................................................................................18



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1 Selecting Application Modes

For heat transfer problems you usually need one of the heat transfer application modes to model the

temperature fields and a fluid dynamics application mode to model the air (or liquid) flow.

If you have Heat Transfer Module, use it's application modes, otherwise use standard package's

modes. Application modes from Heat Transfer Module have more features than the ones from the

standard package.

1.1 Heat Transfer, 2D

Open Model Navigator (File->New).

Select Space Dimensions: 2D.

1.2 Heat Transfer, 3D

Open Model Navigator (File>New).

Select Space Dimensions: 3D.

1.3 Standard Package, Application modes

Comsol Multiphysics->Heat Transfer->Conduction

For heat conduction problems

Contains basic boundary (BC) conditions

heat flux, (convective flux for convection), temperature, insulation, and continuity

Comsol Multiphysics->Heat Transfer->Convection and Conduction

For convective heat problems



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Contains basic boundary conditions

Standard package's Heat Transfer application modes can also model simple radiation term (see heat

flux boundary condition's equation).

Comsol Multiphysics->Fluid Dynamics->Incompressible Navier-Stokes

Laminar, constant temperature flows

Basic boundary conditions:

inflow/outflow velocity, pressure, slip/symmetry, no slip, normal flow/pressure,

neutral

1.4 Heat Transfer Module, Application modes

Heat Transfer>General Heat Transfer

Heat transfer by conduction, convection, and radiation

Convection and conduction terms can be switched on and off in subdomain settings.

More options in boundary conditions including: radiation type and highly conductive layers

Heat Transfer>Non-isothermal Flow

Temperature dependent laminar flow

Laminar inflow/outflow boundary condition

Heat Transfer>k-e Turbulence Model

Turbulent flow

Heat Transfer>Fluid-Thermal Interaction

Ready made multiphysics application modes for combined flow and heat problems

If laminar flow, use non-isothermal flow

If turbulent flow, use turbulence coupling

You can also turn turbulence on/off from Physics>Properties.



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2 Geometry Modeling and CAD Tools

Once CAD file is imported you can edit and modify your geometry as it would been drawn with

Comsol Multiphysics.

2.1 Importing CAD Drawing

Select from menu: File>Import>CAD Data From File.

Supported formats 2D

DXF, GDS, Comsol Multiphysics (*.mphtxt, *.mphbin)

Supported 3D formats

STL, VRML, Comsol Multiphysics

Additional in CAD Import Module IGES (*.igs, *iges)

Parasolid (*.x_b, *x_t, *.xmt_txt, *xmt_bin)

SAT (*.sat, *sab, *.xml)

STEP (*.step, *.stp)

2.2 CAD Import Options

You can import both solid and curve objects and choose how to try convert edges to solids.

Repair tolerance is relative to the dimensions of the CAD drawing (1e-2 == 1%, 1e-3 == 0.1%, 1e-4

= 0.01%).

2.3 Exporting Geometry (DXF)

For exporting 2D geometry objects to a DXF file, select Export>Geometry To File in the File menu.

Then, choose DXF file in the Files of type list and click Save.

In 3D only Comsol Multiphysics formats (*.mphtxt, *.mphbin) are supported.

2.4 Adding Geometric Objects

Drawing tools are found from Draw menu or toolbars.

Click one of the draw buttons to draw by mouse, shift click to specify by coordinates.

Drawing objects (2D):

Rectange/Square or Rectangle/Square (Centered)

Ellipse/Circle or Ellipse/Circle (Centered)

Point and Line

2nd or 3rd Degree Bezier Curve

Drawing objects (3D):

Block, Cone, Cylinder, Ellipsoid, and Sphere



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Point and Line

In addition you can use 2D work planes and embed, extrude or revolve 2D objects into 3D

2.5 Modifying Objects

To modify object

Draw>Object properties

To copy object

Copy - CTRL+C (or Edit>Copy)

Paste - CTRL+V (or Edit>Paste)

Toolbar buttons common for 2D and 3D

Array - create and (copied) array of the selected object(s)

Mirror - copy and flip the selected object(s) around the reflection line

Move - displace the selected object(s) by the specified distance

Rotate - rotate around specified rotation point

Scale - scale the object(s) by the scale factor

2D tools only

Fillet/Chamfer - round the sharp corners

Tangent - create tangent lines between edges and points

2.6 Object Composition

Union, Intersection, Difference - create a composite of selected objects

Create Composite Object - arbitrary composition by using dialog

Coerce to Solid, Coerce to Face (3D only), Coerce to Curve

convert objects to solid, face or curves

Split object

Delete Interior boundaries

2.7 Specifying Grid and Axes

Options>Axes/Grid Settings

2.8 Using Work Planes

Draw>Work Plane Settings

2.9 Using Assemblies

Draw>Use Assembly

Draw>Create Pairs



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2.10 Visualization Tools

Options>Visualization/Selection Settings

Options>View Geometries

Options>Zoom (also in toolbar)

Options>Suppress Options>Labels

3 Modeling Physics and Equations

This chapter explains a range of methods you can use when building models in COMSOL

Multiphysics.

3.1 Entering Material Properties

Select Physics>Subdomain Settings. Material properties can be constants, expressions, or functions.

Subdomains

The model is splitted into subdomain volumes according to geometric boundaries

Groups

You can group and name similar subdomains

Select by group

Select similar subdomains

Active in this domain

Select which subdomains are involved in calculations

Library material

Material properties are taken from material library



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Use Load button to explore the material libraries

Modify material libraries from Options>Material Library

Init

Initial values for modeling

3.2 Specifying Boundary Conditions

Select Physics>Boundary Settings.

Select Boundaries from the list and change the boundary condition from drop down list.

Additional tabs are used for special boundary conditions.



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3.3 Specifying Application Mode Properties

Application Mode specific properties are found from Physics>Properties and unit dependent scalar

variables from Physics>Scalar Variables.



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4 Meshing

4.1 Triangular (free) meshing

Select Mesh>Free Mesh Parameters.

4.2 Quadrilateral (brick, mapped) meshing

Select Mesh>Mapped Mesh Parameters.

4.3 Other Meshing options

The On-line Users Guide illustrates the use of meshing tools with several examples.



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5 Solving the Model

5.1 Solver settings

If you have selected the right analysis type from the Model Navigator, you can just press the Solve

button. To change the analysis type and the solver settings select Solve>Solver Parameters.

5.1.1 Stationary solver settings

Analysis

Sets up equations in the application mode (see also Physics>Properties)

Auto select solver

Analysis type sets up also automatically the solver

Solver

For Heat Transfer problems: Stationary, Time dependent or Parametric

Linear system solver

Try first the default settings, they have been automatically selected according your

application mode selections If you know good settings for your problem, use those

Otherwise see Users Guide>Linear System Solver Selection Guidelines



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5.1.2 Time-dependent solver settings

General page

Times

Syntax: start:step:stop

the default example 0:0.1:1, from 0 to 1 sec with step of 0.1

Relative and Absolute tolerances

Affect on accuracy of the solution in time

Time stepping page

Time steps taken by solver

Use (always) Intermediate, solver is forced to calculate the values at the times you have

specified on the general page, but between those values it can step freely

Advanced pageStore solution on file

Use this if you have problems with out-of-memory



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5.1.3 Parametric solver settings

Give the name of parameter and list of parameter values and you are done.

5.2 Solver Manager

Select Solve>Solver Manager.

By changing Initial values and Solve For Variables you can iteratively and sequentially find a

solution for complex problems.

Initial value

These values affect on the variables you are solving for now



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Initial value expression evaluate the expression in init page (Subdomain and boundary

settings)

Current solution continue from the values you have solved so far

Stored solution used together with the Store Solution button, you can store one previous

solution, which is different from current solution

Values of variables not solved and linearization point

If you are solving your model sequentially, used combination with Solve for Variables page

Use settings from Initial value frame use same setting as for initial value

5.3 Quick and Easy Solutions

Changing element type

Select Physics>Subdomain settings and change the element type to linear

Static problem

Use nonlinear solver (GMRES, Conjugate Gradients, Geometric Multigrid)

Increase Relative Tolerance in Solver Parameters>Stationary page

Drop maximum number of iteration value, try for example, 1 (!)

Time-dependent problem

Increase relative and absolute tolerance in Solver Parameters



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6 Postprocessing and Visualization

6.1 Plot Parameters

To change the default postprocessing plot select Postprocessing>Plot Parameters.

Predefined quantities

Lists predefined quantities

Expression

Enter custom expression

Example: sqrt(T)+3

Unit

For predefined expressions you can select unit from the list

Color scale

Adds a scale to right of the postprocessing graphics



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General settings

Plot type

Check those plots you want to display simultaneouslySolution to use

For time-dependent and parametric models you can select the solution (time or parameter

value)

Element selection

In 3D cases can be used for select part of the geometry

Example: x > 0.05 (select the elements having x-coordinate greater than 0.05)

Plot in

Either to main GUI or separate figures



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6.2 Creating Animations

You can create animations for time-dependent and parameteric studies by selecting Animatepage

from Postprocessing>Plot Parameters.

Solutions to use

Select the solutions to animation

Use camera settings from main window

Use the axis settings from GUI

Start Animation

Create the movie

Movie Settings

Select the movie type, resolution

Press Advancedbutton to change encoder and compression level.



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7 Documentation and Model Management

7.1 Creating HTML Summary

Select File>Generate Report.

7.2 Adding Model Description

Select File>Model Properties, and Description settings.

This with the the model image are shown in Model Navigator's User Models page.

7.3 Adding Model Image

Click File>Save Model Image.

7.4 Maintaining User Model Library

Select File>Open Model Library.

Select User Models page.

ClickLibrary root button

Select the root of your own model

Keep all your models in one structured folder, for example C:\models. Use that as the Library rootof User models. Create subfolders for each new project and keep all project related model in same

folder. Use numbering for versions and remember enter Model Description and update the model

image before saving new version.

http://c/modelshttp://c/models

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